Cement clinker is produced by sintering a raw material, such as limestone mixed with silica, alumina and iron oxide, in a rotary kiln. The production may take place using a dry, semi-wet, or wet process, or in a rotary kiln that receives heated and dried raw material from a Lelep-Lepol travelling grate.
In the dry process, the raw material passes through a series of cyclones and preheaters that heat the raw material, and through a precalciner that further preheats and precalcines the raw material. The heated and precalcined raw material then enters a rotary kiln in which it is sintered in a sinterization or klinkerization reaction to form cement clinker. The cement clinker is then cooled in a grate cooler and discharged.
In the wet process, the raw material is mixed with water at a grinding step to form a slurry having a water content of approximately 35-40%. The slurry then is passed through a long rotary kiln having a series of zones, which function as chambers, to form cement clinker.
A typical wet process kiln has a fuel consumption per kilogram of clinker produced of between 1,300 and 1,500 kilocalories, depending on the water content of the slurry fed to the kiln. The fuel consumption is approximately 175% of the consumption of a dry process rotary kiln that is equipped with a preheater and precalciner. A kiln having a capacity to produce 1,500 tons of clinker per day typically has a diameter of between four and five meters and a length of between 135 and 150 meters.
The semi-wet process of producing cement clinker involves using a slurry of raw material and water in which the water content is in the range of approximately 15% to 20%. The kiln is equipped with filters that remove a portion of the water from the slurry before it is fed into the kiln.
In a process using a rotary kiln and a Lelep-Lepol travelling grate, the raw material is fed onto the grate in granulated (i.e., nodulized) form and hot gases from the kiln are pulled through the grate to heat and dry the nodules of raw material. The raw material, still in the form of nodules, is then fed into the rotary kiln where the raw material is decarbonated, heated, sintered, and fed into a clinker grate cooler.